The present invention relates to power electronics apparatus and methods and, more particularly, to apparatus and methods for monitoring parallel-connected power switching devices.
Power conversion apparatus, such as uninterruptible power supply (UPS) apparatus, often employ power switching devices to perform power conversion operations, such as rectification or inversion. For example, a typical double conversion UPS may include an inverter and/or a rectifier including power transistors, such as insulated gate bipolar transistors (IGBTs), arranged in a half-bridge C configuration. Such an IGBT may be driven by driver/monitor circuits that include circuitry for driving a gate or base terminal of the power transistor, along with circuitry for monitoring collector-emitter voltage for short circuit detection, as described in U.S. Pat. No. 6,741,116 to Herzer et al. and U.S. Pat. No. 6,851,077 to Herzer et al. An article by Lehmann et al. entitled “Method for Electrical Detection of End-of-Life Failures in Power Semiconductors,” published in 2003 by Semikron Elektronik GmbH at www.semikron.com describes techniques for detecting emitter and gate bond wire liftoff in IGBTs that makes use of gate driver circuitry.
In high-capacity applications, multiple power switching devices, e.g., IGBTs, may be connected in parallel to provide increased current capacity, as shown, for example, in U.S. Pat. No. 6,518,821 to Jeorg and U.S. Pat. No. 5,949,273 to Mourick et al. In particular, large-scale UPSs may utilize rectifier or inverter modules with converter circuits that contain IGBT modules having multiple IGBTs that are configured to allow connection in parallel configurations. Examples of such a multi-IGBT modules are the SixPACK IGBT modules distributed by eupec, Inc. and described at www.eupec.com. These SixPACK modules include six IGBTs that are configured to allow connection in a half-bridge arrangement of two groups of three parallel-connected IGBTs. Multiple ones of such IGBT modules may be further connected in parallel to construct, for example, a high-capacity rectifier or inverter module. Such rectifier and inverter modules may be further paralleled to provide even greater capacity.